Formation of packaging material

ABSTRACT

A pattern is formed in rapid and continuous manner on aluminized polymer film by printing the aluminum surface with a sodium hydroxide-resistant material, which may be pigmented, contacting the non-overprinted areas of the aluminum with hot aqueous sodium hydroxide solution to dissolve the aluminum rapidly from the base polymeric film and leave unaffected the overprinted areas, and washing the spent sodium hydroxide solution from the film. The steps are carried on a continuous web of aluminized film and result in pattern of opaque areas and transparent areas, corresponding to the overprinted and non-overprinted areas of the film.

FIELD OF INVENTION

The present invention relates to packaging material, in particularmetallized plastic film.

BACKGROUND TO THE INVENTION

Metallized plastic film material is used for a wide variety of packagingoperations. The film is made by vapor depositing a layer of the metal,usually aluminum, on the polymeric substrate, and it has previously beensuggested to mask portions of the polymer substrate to prevent metalvapor deposition thereon and thereby provide a transparent area orwindow through which product packaged in a package formed from the filmmay be viewed. The major problem with the provision of such windows islack of color compatibility for colors which are printed both on thewindow area and the metallized area. Further, patterns more intricateother than simple windows have not been produced on metallized plasticfilm by this masking method.

It has previously been suggested in U.S. Pat. No. 4,242,378 to provide apattern of see-through portions and opaque portions on a metallizedplastic film by forming a pattern of a water-insoluble resin on themetal layers corresponding to the opaque portions and immersing theresulting film in an aqueous solution of a metal solubilizer to dissolvethe exposed metal while leaving untouched the patterned portion to formthe see-through portion in the dissolved metal areas. Although thisprocess is capable of producing colored printing by using resin-basedprinting inks, the procedure is time consuming and incapable of rapidcontinuous operation.

SUMMARY OF INVENTION

In accordance with the present invention, there is provided a method ofprinting on a metallized polymer film, which comprises applying patternof etchant-resistant material to the metal surface of the polymer film,contacting the metal surface with an etchant solution to dissolve themetal from the film, and washing the surface free of etchant solution.

The method of the invention is effected under critical etchantconditions to achieve rapid and continuous operation. The etching stepis effected using sodium hydroxide solution which may have an NaOHconcentration of up to 25% by weight, preferably in the range of about 5to about 10% by weight.

The time required for application of the sodium hydroxide solution tothe printed film to etch the exposed metal surface from the polymer filmdepends to some extent on the temperature of the sodium hydroxidesolution. Temperatures in the range of about 15° to about 100° C. may beused with treatment times varying in temperature dependant manner in therange of about 10 seconds to about 0.1 second. For continuous operation,it is preferred to maintain the contact time quite short, and hence itis preferred to use a temperature of above about 50° C.

The procedure is effected continuously by drawing a web of metallizedplastic film from a source roll and conveying the web successively pasta printing station, an etchant application station and a washingstation, before being dried and reeled onto a take-up roll. The webspeed may be varied widely up to about 1000 ft/min, preferably in therange of from about 100 to about 700 ft/min.

BRIEF DESCRIPTION OF DRAWING

The sole FIGURE of the drawing is a schematic representation of anapparatus for effecting the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawing, a continuous web 12 of metallized polymer filmis drawn from a roll 10. Any desired polymeric material may be used asthe base film, including polyethylene, polypropylene, polystyrene,polyester, polyvinyl chloride and polycarbonate. The base film may beany desired thickness sufficient to enable a suitable packaging materialto be formed therefrom, preferably about 10 to about 50 microns.

The metal layer, which is provided on one face of the polymeric film, isobtained by vacuum coating in well known manner. The thickness of themetal film may vary widely within the range from about 10 to about 1000A, preferably about 300 to 600 A. Aluminum is usually the metal.

The continuous web 12, in which the metal film faces downwardly as seenin the FIGURE is conveyed past a printing station 14 whereat a patternof etchant-resistant material is printed on the metal layer from aprinting roller 16. The etchant-resistant material may be awater-insoluble resinous material and may be pigmented or clear, inaccordance with the appearance of the pattern desired on the metallayer.

Etchant-resistant material is applied to a pattern provided on thesurface of roller 16 by pick up from a bath 18 of etchant-resistantmaterial. The roller 16 is backed by a backing roller 20. The web 12leaving the printing station 14 bears a predetermined pattern ofetchant-resistant material overlying the metal layer, with areas ofexposed metal layer between the portions of etchant-resistant materialoverlying the metal layer.

The patterned web is next conveyed past an etchant-applying station 22whereat sodium hydroxide solution is applied to the patterned web acrossthe whole width thereof from a wet roller 24. The wet roller 24 usuallyis heated to an elevated temperature, preferably in the range of about50° to about 90° C., so that the aqueous sodium hydroxide solution isapplied by the wet roll 24 hot to the web 12 engaged by the roll 24. Abackup roller 28 is provided to assist in application of sodiumhydroxide solution.

The sodium hydroxide solution of desired concentration, preferably about5 to about 10% by weight, is provided on the surface of the roller 24 bypick up from a bath 26 of sodium hydroxide solution.

Application of the hot sodium hydroxide solution across the width of theweb 12 commences etching of the aluminum layer from the base film inthose areas where the aluminum is exposed to the solution. Theetchant-resistant printed areas are not affected by the sodium hydroxidesolution and hence the aluminum located under the etchant-resistantmaterial remains in contact with the base film.

The dissolving of the exposed aluminum in the sodium hydroxide solutionoccurs as the web 12 travels along its horizontal path beyond theetchant-applying station 22 and is complete rapidly. In order to requireonly a minimum of floor space, the travel path of the etchant-appliedweb beyond the station 22 is maintained quite short by balancing thefactors of web speed and etchant temperature and concentration.

In addition, the web 12 may pass through an air tunnel 30, through whichheated air may flow, to assist in the rapid completion of the etchingprocedure.

Upon completion of the etching, the web 12 is washed at washing station32. Water is applied to the web 12 by a squeegee-type roller 34 whichdips into a bath 36 of water. The spent wash water flows back into thebath 36. As a wash water is applied, the web 12 passes round a takeuproller 38. The washed web may be dried by a hot air drier 40, if desiredwith the assistants of an air doctor 42 before passage to a take-up roll(not shown).

The washed and dried web comprises an opaque pattern corresponding tothe pattern printed thereon at the printing station 14 and transparentareas between the opaque pattern comprising base film from which thealuminum has been removed. The procedure produces in rapid continuousmanner a patterned polymeric film suitable for use as a packagingmaterial.

Since the film is printed with the desired pattern, which may be simpleor intricate, or may be transparent or pigmented, the prior art problemsof color matching and the inability to produce intricate patterns whenthe masking technique is used are overcome. Further, the procedure ofthe invention is rapid and continuous, and thereby overcomes theproblems of U.S. Pat. No. 4,242,378.

EXAMPLE

Aqueous sodium hydroxide solution at concentration of 5 wt % NaOH and 10wt % NaOH was applied to aluminized Mylar (trade mark) film at varioustemperatures and the period of time for complete removal of the aluminumfrom the film was determined.

The results obtained are set forth in the following Table:

                  TABLE                                                           ______________________________________                                                        NaOH Solution                                                 Temperature     (secs)                                                        °C.      5 wt %  10 wt %                                               ______________________________________                                        50              5.5     3.8                                                   60              3.5     2.1                                                   70              2.2     1.3                                                   80              1.5     1                                                     90              1       0.5                                                   ______________________________________                                    

The very rapid removal of the aluminum from the foil, demonstrated bythe results of the Table, indicates that continuous high speedproduction of patterned film can be attained using elevated temperaturesand moderate sodium hydroxide concentrations.

SUMMARY OF DISCLOSURE

In summary of this disclosure, the present invention provides animproved method of patterning aluminized polymeric film which issuperior to prior procedures. Modifications are possible within thescope of the invention.

What I claim is:
 1. A continuous method of forming a repetitive patternon a roll of aluminized polymer film which comprises:(a) continuouslyfeeding a web of said aluminized polymer film from said foll at a webspeed of up to about 1000 ft/min; (b) printing said web with a patternof etchant-resistant material corresponding to the pattern desired onthe aluminized surface thereof; (c) applying aqueous sodium hydroxidesolution having a concentration of up to about 25 wt % at a temperatureof about 15° to about 100° C. across the whole width of the web tocontact the pattern on the web; (d) allowing said sodium hydroxidesolution to remain in contact with said web as it is conveyed for about0.1 to about 10 seconds to permit said sodium hydroxide to dissolvealuminum only from areas of said web not having said pattern ofetchant-resistant material applied thereto; (e) washing the spent sodiumhydroxide solution from said web to leave said pattern ofetchant-resistant material on a transparent polymeric film; and (f)drying the resulting washed web.
 2. The method of claim 1 wherein saidweb speed is about 100 to about 700 ft/min.
 3. The method of claim 2wherein said sodium hydroxide has a concentration of about 5 to about 10wt %.
 4. The method of claim 3 wherein said sodium hydroxide solutionhas a temperature of about 50° to about 90° C.
 5. The method of claim 1,2, 3 or 4 wherein said etchant-resistant material is pigmented.
 6. Themethod of claim 4 wherein said pattern is printed on said web by arotary printing surface bearing said etchant-resistant material in saidpattern and engaging said web.
 7. The method of claim 1 wherein saidsodium hydroxide solution is applied from a rotary surface which is wetwith said sodium hydroxide solution.
 8. The method of claim 7 whereinsaid rotary surface is heated to provide said sodium hydroxide solutionat the desired temperature.